Intelligent soldering cartridge for automatic soldering connection validation

ABSTRACT

An intelligent soldering cartridge that includes: a housing; a solder tip; a heater for heating the solder tip; a storage device for storing information about characteristics of the cartridge; a processor for retrieving the information about characteristics of the cartridge, monitoring the power level delivered to the solder tip to detect liquidus occurrence at a solder joint, determining a thickness of an intermetallic compound (IMC) of the solder joint using some of the retrieved information, determining whether the thickness of the IMC is within a predetermined range, and generating an indication signal indicating that a reliable solder joint connection is formed when the thickness of the IMC is within the predetermined range; and an interface for transmitting the indication signal.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is a Continuation of patent application Ser. No.14/966,975, filed on Dec. 11, 2015, which is a Continuation-In-Part ofpatent application Ser. No. 14/794,678, filed on Jul. 8, 2015 andentitled “Soldering Iron With Automatic Soldering ConnectionValidation,” which claims the benefit of the filing date of U.S.Provisional Patent Application Ser. No. 62/033,037, filed on Aug. 4,2014 and entitled “Connection Validation For Handheld Soldering IronStation,” the entire contents of which are herein expressly incorporatedby reference.

FIELD OF THE INVENTION

The present invention relates generally to manufacturing, repair andrework of printed circuit boards (PCBs), and more particularly to asoldering station with automatic soldering connection validation.

BACKGROUND

With the greater variety of components used on printed circuit boards(PCBs), smaller passive components and larger ICs with finer ball pitchdimensions, the demands on high quality solder joints to aid PCBassembly (PCBA) fabrication and rework have increased. Faulty solderjoint has cost companies billions of dollars over the years. Manyprocesses have been developed to reduce failure rate for wave soldersystems. However, for point to point handheld soldering and reworkapplications, companies are relying on operators' skills to produce goodsolder joints with quality electrical connections. Regardless of howmuch training is provided to the operators of the soldering iron,without guidance during a soldering activity, the operators may make andrepeat mistakes due to the fact that there are many factors that impactheat transfer by the soldering iron for forming a solder joint with goodelectrical connection. These factors include solder tip temperature,geometry of the solder tip, oxidation of the solder, human behavior, andthe like.

Moreover, automatic (e.g., robotic) soldering is currently strictly anopen-loop time based event, where a robot moves to the specific joint,the solder tip is automatically placed on the joint, solder isautomatically applied, and a prescribed time later (determined by aspecific software for the robot), the solder tip is automaticallyremoved from the joint. This process is repeated until the robot'sprogram is complete. This open-loop time based event can besignificantly improved by using the various embodiments of connectionvalidation (CV) technology disclosed herein, with a real-time feedbackof the solder quality.

SUMMARY

In some embodiments, the present invention is an intelligent solderingcartridge that includes: a housing; a solder tip; a heater for heatingthe solder tip; a storage device for storing information aboutcharacteristics of the cartridge; a processor for retrieving theinformation about characteristics of the cartridge, monitoring the powerlevel delivered to the solder tip to detect liquidus occurrence at asolder joint, determining a thickness of an intermetallic compound (IMC)of the solder joint using some of the retrieved information, determiningwhether the thickness of the IMC is within a predetermined range, andgenerating an indication signal indicating that a reliable solder jointconnection is formed when the thickness of the IMC is within thepredetermined range; and an interface for transmitting the indicationsignal.

In some embodiments, the present invention is an intelligent solderingcartridge that includes: a housing; a solder tip; a heater for heatingthe solder tip; a storage device for storing information aboutcharacteristics of the cartridge; a processor for retrieving theinformation about characteristics of the cartridge, detecting liquidusoccurrence at a solder joint, receiving a 3D current image of the solderjoint, determining volume of the dispensed solder after occurrence ofthe liquidus from the 3D current image, comparing the volume of thedispensed solder to an amount of solder needed to fill in a barrel of ahole for a through hole component, or to fill in a surface of a barrelof a hole for a surface mount component to determine how much of thedispensed solder is dissipated onto the barrel or on the surface area ofthe barrel, repeating the comparing of the volume of the dispensedsolder until the dispensed solder has filled the barrel or the surfacearea of the barrel, and generating an indication signal indicating thata reliable solder joint connection is formed when the dispensed solderhas filled the barrel or the surface area of the barrel within thepredetermined tolerance; and an interface for transmitting theindication signal.

The interface may be a wireless and/or wired interface. In someembodiments, the cartridge includes a temperature sensor for measuring atemperature of the solder tip, where the temperature sensor periodicallymeasures the temperature of the solder tip and feeds the information tothe processor, and wherein the processor adjusts the temperature of thesolder tip when said temperature changes from a predetermined value.

The intelligent soldering cartridge of the present invention may be usedin a handheld soldering iron or an automatic soldering station forsoldering work pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A depicts an exemplary handheld soldering iron, according to someembodiments of the present invention.

FIG. 1B is an exemplary block diagram of a processor and associatedcomponents, according to some embodiments of the present invention.

FIG. 1C depicts an exemplary handheld soldering iron where the processorand associated circuitry are in a power supply, according to someembodiments of the present invention.

FIG. 1D shows an exemplary handheld soldering iron where the processorand associated circuitry are in a handpiece, according to someembodiments of the present invention.

FIG. 1E illustrates an exemplary handheld soldering iron where theprocessor and associated circuitry are in a cartridge, according to someembodiments of the present invention.

FIG. 1F shows an exemplary handheld soldering iron where the processorand associated circuitry are in a work stand, according to someembodiments of the present invention.

FIG. 1G depicts an exemplary automatic soldering station, according tosome embodiments of the present invention.

FIG. 2 shows an exemplary process flow, according to some embodiments ofthe present invention.

FIG. 3A shows a graph for a change in temperature of a soldering tipover time, for three given load sizes, according to some embodiments ofthe present invention.

FIG. 3B depicts a graph for a change in impedance of a soldering tipover time, for three given power levels and three given temperatures,according to some embodiments of the present invention.

FIG. 4A illustrates a graph for the thickness of the IMC versus time,according to some embodiments of the present invention.

FIG. 4B illustrates a graph for the thickness for the IMC versussoldering time, according to some embodiments of the present invention.

FIG. 4C shows an IMC layer for a soldering event.

FIG. 5 is an exemplary process flow for liquidus detection andconnection verification using images from a plurality of cameras,according to some embodiments of the present invention.

FIGS. 6A-6D show various images used for detection of liquidus,according to some embodiments of the present invention.

FIG. 7A shows some exemplary solder joints for through hole components,according to some embodiments of the present invention.

FIG. 7B depicts some exemplary solder joints for surface mountcomponents, according to some embodiments of the present invention.

FIG. 8 shows an exemplary intelligent soldering cartridge, according tosome embodiments of the present invention.

DETAILED DESCRIPTION

In some embodiments, the present invention is a soldering station withautomatic soldering connection validation. The soldering stationincludes a processor, such as a microprocessor or controller, memory,input/output circuitry and other necessary electronic circuitry toperform the soldering connection validation.

In some embodiments, the processor receives various characteristics ofthe solder joint and soldering station and performs a process ofcalculating the intermetallic compound (IMC) thickness of solder and PCBsubstrate to ensure a good solder joint is formed during a solderingevent. Once a good electrical connection for the solder joint isconfirmed, an audio, LED, or vibration indicator in the solderingstation, for example, in a handpiece or on a display in a solderingstation, informs the operator or a soldering robot program of theformation of the good solder joint. Typically, a good solder jointformed by SAC (tin-silver-copper) solder and copper substrate PCB iswhen the intermetallic thickness of the solder is between 1 um-4 um.Accordingly, if the soldering station uses, for example, SAC305 (96.5%Sn, 3% Ag, 0.5% Cu) solder wire with copper substrate PCB, the IMCthickness of the Cu₆Sn₅ is calculated by some embodiments of the presentinvention and the operator or the robot is notified once the IMCthickness of the solder reaches 1 um-4 um, during the soldering event.

The chemical reaction between the copper substrate and the soldering canbe shown as:3Cu+Sn->Cu₃Sn (phase 1)  (1)2Cu₃Sn+3Sn->Cu₆Sn₅ (phase 2—IMC thickness is 1 um-4 um)  (2).

Phase 1 of the chemical reaction is temporary (transient) and thereforeis not used for determination of the quality of the solder joint.

FIG. 1A depicts an exemplary handheld soldering iron, according to someembodiments of the present invention. As shown, the handheld solderingiron includes a power supply unit 102 including a display 104, forexample an LCD display, and various indicators 106, such as LEDindicators 106 a and 106 b. Other indicators, such as sound-emittingdevices or haptic devices can be used as well. The soldering ironfurther includes a handpiece 108 coupled to the power supply unit 102and a (work) stand 11 that accommodates the handpiece 108. The handpiece108 receives power from the power supply unit 102 and heats a solderingtip attached to or located in a soldering cartridge to perform thesoldering on a work piece. In some embodiments, the soldering cartridgemay include a temperature sensor thermally coupled to the soldering tipto sense the tip temperature and transmit that data to a processor.

The handpiece 108 may include various indicators such as one or moreLEDs and/or a buzzer on it. In some embodiment, the power supply unit102 or the handpiece 108 includes a microprocessor, memory, input/outputcircuitry and other necessary electronic circuitry to perform variousprocesses. One skilled in the art would recognize that themicroprocessor (or the controller) may be placed in the power supply, inthe handpiece, or a stand of the soldering system. Communication withexternal devices, such as a local computer, a remote server, a robot forperforming the soldering, a printer and the like, may be performed atthe work stand by wired and/or wireless connections, using the knownwired and/or wireless interfaces and protocols.

In some embodiments, the microprocessor and the associated circuitsidentify what soldering cartridge is being used, validate the tipgeometry, validate that the temperature and load (solder joint) arematched to ensure that the selected soldering cartridge can producesufficient energy to bring the load to the melting point of the solder,detect liquidus temperature and then determine the IMC thickness of thesolder, as described in more detail below. For example, if the tipgeometry is too small for the load, the tip would not be able to bringthe joint to the solder melting point. The liquidus temperature is thetemperature above which a material is completely liquid. Liquidustemperature is mostly used for impure substances (mixtures) such asglasses, alloys and rocks. Above the liquidus temperature the materialis homogeneous and liquid at equilibrium. Below the liquidustemperature, crystals are formed in the material after a sufficienttime, depending on the material.

FIG. 8 shows an exemplary intelligent soldering cartridge, according tosome embodiments of the present invention. In some embodiments, theintelligent soldering cartridge includes a soldering tip 802, associatedwiring 804, a magnetic shield 806, a heater 808 to heat the tip, a shaftor housing 810, connector(s) 812 for both electrical and mechanicalconnections and a storage device 814 such as a non-volatile memory(NVM). The intelligent soldering cartridge may further include one ormore sensors 818, such as temperature sensor to measure the temperatureof the tip and/or a potentiometer to measure the impedance of the tip, aradio frequency identification device (RFID) 820, and/or a processor andassociated circuitry 816 such as input/output circuits and wired and/orwireless interfaces to data communication. The mechanical connector (notshown) for connecting the cartridge to a hand-piece or robot arm may beincluded for efficient, quick-release operation.

In some embodiments, the cartridge ID, for example, a serial number or acode unique to the specific cartridge, is read from the NVM 814 or RFID820 to identify the cartridge, its type and related parameters andspecification information. The NVM 814 may also store information abouta change in temperature of a plurality of soldering tips over time,similar to the graphs of FIGS. 3A, 3B, 4A and 4B. Once a specificsoldering tip is used, the information about the change in temperatureof the tip being used is retrieved form the NVM. Typically, during asoldering event, the temperature of the tip drops as it heats the solderjoint and thus the heater needs to reheat the tip, which often resultsin overshooting the required (set) temperature for the tip. However, insome embodiments, a temperature sensor 818 periodically senses thetemperature of the tip and feeds the information to the processor (ordirectly to the heater 808) to adjust the temperature in case of anytemperature drop (or increase) due to the load or other factors. Thisway, an appropriate amount of heat is directly delivered to the solderjoint.

In some embodiments, the NVM and/or the RFID stores data related tocharacteristics of the cartridge such as, part number, lot code, serialnumber, total usage, total point, tip mass/weight, tip configuration,authentication code (if any), thermal efficiency, thermalcharacteristic, and the like. This data may be retrieved by a processor(e.g., the internal processor 816 or an external processor) periodicallyat the startup and during the soldering operation. In some embodiments,the data may also be received and transmitted via wired or wirelessmethods.

In some embodiments, the NVM and/or the RFID of the cartridge includesall or some of the following information.

-   -   1. Temperature of the heater/tip and optionally information        about a change in the temperature over time for various load        sizes;    -   2. Tip geometry, which may include contact surface of the tip        with the solder, distance of the tip from the heater, mass of        the tip;    -   3. Thermal efficiency factor of the tip (based on mass, shape,        heater, etc.);    -   4. Number of soldering events that have been performed by the        specific tip, which may be used for traceability    -   5. Time of tip usage (for example, total time of the tip being        usage for warranty and traceability)    -   6. Date of manufacturing of the cartridge    -   7. Serial number and identification code for the cartridge    -   8. Part-number    -   9. CV selection flag (whether the tip and/or cartridge is        subject to CV technology)    -   10. Data Checksum

Tip temperature, tip geometry and thermal efficiency are used tocalculate an approximation for the IMC layer thickness, as explainedbelow. Number of soldering events, time of tip usage and date ofmanufacturing can be used to further refine the process of IMC thicknesscalculation, as explained below. The historical information, such asusage time, number of soldering events and the like may be written backto the NVM to be accumulated.

Serial number, part number and CV selection flag are for housekeeping,traceability and/or determination of whether the process will can/shouldprovide a valid indication of the IMC formation. Data checksum may beused to determine if there is a failure in the NVM or communication datatransfer error, in some embodiments. In some embodiments, theintelligent cartridge for a robot soldering station includes ananti-rotation D ring for preventing the cartridge from unwantedrotations, when the robot arm is being rotated.

In some embodiments, the intelligent soldering cartridge is capable ofperforming the processes of liquidus detection and connectionverification according to both process flows of FIGS. 2 and 5. Forexample, the processor 816 is capable of retrieving the informationabout characteristics of the cartridge from the NVM or RFID, detectingliquidus occurrence at a solder joint, receiving a 3D current image ofthe solder joint, determining volume of the dispensed solder afteroccurrence of the liquidus from the 3D current image, comparing thevolume of the dispensed solder to an amount of solder needed to fill ina barrel of a hole for a through hole component, or to fill in a surfaceof a barrel of a hole for a surface mount component to determine howmuch of the dispensed solder is dissipated onto the barrel or on thesurface area of the barrel, repeating the comparing of the volume of thedispensed solder until the dispensed solder has filled the barrel or thesurface area of the barrel, and generating an indication signalindicating that a reliable solder joint connection is formed when thedispensed solder has filled the barrel or the surface area of the barrelwithin a predetermined tolerance.

In addition, the processor 816 may be capable of retrieving theinformation about characteristics of the cartridge, detecting liquidusoccurrence at a solder joint, receiving a 3D current image of the solderjoint, determining volume of the dispensed solder after occurrence ofthe liquidus from the 3D current image, comparing the volume of thedispensed solder to an amount of solder needed to fill in a barrel of ahole for a through hole component, or to fill in a surface of a barrelof a hole for a surface mount component to determine how much of thedispensed solder is dissipated onto the barrel or on the surface area ofthe barrel. The processor may then repeat the comparing of the volume ofthe dispensed solder until the dispensed solder has filled the barrel orthe surface area of the barrel, and generating an indication signalindicating that a reliable solder joint connection is formed when thedispensed solder has filled the barrel or the surface area of the barrelwithin the predetermined tolerance.

FIG. 1B is an exemplary block diagram of a processor and associatedcomponents, according to some embodiments of the present invention. Asillustrated, a processor 112, a memory 114 a non-volatile memory (NVM)116 and an I/O interface 118 are coupled to a bus 120 to comprise theprocessor and associated circuitry of some embodiments of the presentinvention. The I/O interface 118 may be a wired interface and/or awireless interface to components external to the soldering station.Optionally, one or more cameras 122 and 124 are coupled to the processorand the memory via the bus 120 or the I/O interface 118 to captureimages from a solder joint from various viewpoints. Additionally, anoptional temperature sensor 126 for sensing the temperature of thesoldering tip may be coupled to the processor 112 and the memory 114 viathe bus 120 or the I/O interface 118. The optional temperature sensormay be located at or near the soldering tip.

As one skilled in the art would readily understand, different componentsdepicted in FIG. 1B may be located in different parts of the solderingiron or automatic soldering station, as partly explained below. Forexample, the cameras may be located outside of and decoupled from thedifferent components of the soldering iron or automatic solderingstation, while the processor and associated circuitry may be located inany components of the soldering iron or automatic soldering station (asdescribed below). The sensors may also be located in/at differentcomponents of the soldering iron or automatic soldering station,depending on their applications.

FIG. 1C depicts an exemplary handheld soldering iron where the processorand associated circuitry are in a power supply, according to someembodiments of the present invention. As shown, the power supply unitincludes the processor and associated circuitry and an internal powermonitoring unit/circuit to detect and change the power supplied by thepower supply to the handpiece, cartridge and/or the soldering tip. Thepower supply unit also includes wired and/or wireless interface(s) toelectronically communicate with the handpiece, the LEDs, the cartridgeand/or external devices. Once the processor determines the quality ofthe solder joint, it outputs an appropriate signal to activate one ormore of an LED, a sound-emitting device, and a haptic device to notifythe operator about the determined quality of the solder joint.

Moreover, the cartridge ID, for example, a serial number or a codeunique to the specific cartridge, is read from the memory (e.g., NVM orRFID) of the cartridge to identify the cartridge and its type. This maybe done by a wired or wireless connection. For instance, in the case ofan RFID within the cartridge, the RFID (or even the NVM) may be read (bythe processor) wirelessly. Once the intelligent soldering cartridge andits type are identified, the relevant parameters of the cartridge areretrieved by the processor from a memory, for example, an EEPROM. Thememory that stores the cartridge related parameters may be in or outsideof the cartridge. In some embodiments, if all of the related (cartridge)parameters are stored in a memory (which is in the cartridge), thecartridge may not need to be specifically identified since theparameters are already available in the memory of the cartridge and arespecific to the cartridge.

In some embodiments, the cartridge may have a barcode, a magnetic stripeor a “smart chip” to identify the cartridge. Once the cartridge isidentified, the relevant information may be read from the barcode, themagnetic stripe, the smart chip or fetched from an outside storage, suchas a memory or a database coupled to a computer network, such as theInternet. For the purpose of the present application and the claimedinvention, a storage device would also include a barcode, a magneticstripe and a smart chip.

FIG. 1D shows an exemplary handheld soldering iron where the processorand associated circuitry are in the handpiece, according to someembodiments of the present invention. The general functions andoperations of these embodiments are similar to those explained withrespect to FIG. 1C, except that the processor (and associated circuitry)and the power monitor unit/circuit are now located with the handpiece.

FIG. 1E illustrates an exemplary handheld soldering iron where theprocessor and associated circuitry are in a cartridge, according to someembodiments of the present invention. In these embodiments, thecartridge may be similar to the intelligent cartridge depicted in FIG. 8and explained above. The general functions and operations of theseembodiments are similar to those explained with respect to FIG. 1C,except that the processor (and associated circuitry) and the memory arenow located with the cartridge. Again, the communications between thecartridge, the handpiece and external devices may be wired and/orwireless. As one skilled in the art would readily recognize, the powermonitoring unit/circuit (not shown) may be located in the power supplyunit, the handpiece or the cartridge itself. In these embodiments, thedevices that notify the operator (e.g., LEDs, sound-emitting device,and/or haptic devices) may be located with the handpiece or thecartridge itself. If located with the handpiece, the handpiece includesa wired and/or wireless interface to communicate with the cartridge (andany relevant external devices).

FIG. 1F illustrates an exemplary handheld soldering iron where theprocessor and associated circuitry are in a cartridge, according to someembodiments of the present invention. The general functions andoperations of these embodiments are similar to those explained withrespect to FIG. 1C, except that the processor (and associated circuitry)and the power monitor unit/circuit are now located with the work standof the soldering iron.

FIG. 1G shows an exemplary automatic soldering station, according tosome embodiments of the present invention. In these embodiments, thehandpiece and the cartridge are assembled on or part of a robot arm asshown. As shown, a robot arm 140 is capable of three-dimensionalmovements and rotations. A hand-piece 144 is coupled to the robot armand an intelligent soldering cartridge, for example, an intelligentsoldering cartridge according to FIG. 8 is connected to the hand-piece.In some embodiments, the intelligent soldering cartridge 142 may bedirectly coupled to the robot arm 140, which would be acting as thehand-piece.

A work piece 154, such as a printed wiring board (PWB), is placed on amoving platform 156 to have a soldering operation performed thereon. Asolder feeder 146 provides solder to the work piece 154 via a grip,anchor, roller or tube 148. One or more cameras 152 placed at differentangles capture the close up of the solder joint on the work piece. Apower supply 150 provides power to the cartridge and related electronicstherein.

This way, the CV technology of the present invention is capable ofproviding feedback (a closed-loop system) to any conventional automaticsoldering station. For example, the open-loop time based event of theconventional approaches is significantly improved by providing areal-time feedback of the solder quality. That is, instead of using aprescribed time for a solder joint, the CV technology provides the robotmotion control system with a feedback signal that indicates when a goodjoint has been made. In some embodiments, only upon the indication of agood joint, the robot can move to the next joint in the program. When abad joint has been made, the robot stops immediately or at the end ofthe program and alerts the operator of an issue with the solder joint.

FIG. 2 shows an exemplary process flow, according to some embodiments ofthe present invention. As shown in block 202, the process for validatingall the connection joints between the component and the PCB substratestarts. In block 204, the cartridge being used is identified and thedata related to the identified cartridge is retrieved from anon-volatile memory (NVM), such as an EEPROM, in the cartridge oroutside of the cartridge. As described above, in some embodiments, thedata related to the identified cartridge is retrieved, by the processor,from the NVM in the cartridge.

In block 206, the process (e.g., processor) checks the power level todetermine whether any soldering action is being performed, within aperiod of time. If no soldering action to be performed yet, the processwaits in block 206. For example, a timer can be set to a predeterminedtime and if no action happens within that time, the process waits.However, if a soldering action is to be performed, the process proceedsto an optional block 208, where the indicators are reset.

FIG. 3A shows a graph for a change in temperature of a soldering tipover time, for three given solder load sizes. As describe above, thisdata may be stored in the memory of the cartridge. Graph 306 is for alarge load size (e.g., ˜104 Cu Mil²), graph 304 is for a medium loadsize (e.g., ˜54 Cu Mil²) and graph 302 shows a small load size (e.g.,˜24 Cu Mil²). As illustrated in FIG. 3A, for a given tip, the heavierthe load, the higher temperature drop. In some embodiments, if the tiptemperature drop is greater than a predetermined value, for example,around 25° C. (determined by experimental data), the process is abortedsince the power supply would be unable to recover fast enough tocontinue delivering power to the tip to maintain the temperature of thetip, within the required time to complete the soldering event (e.g., 8seconds).

In some embodiments, the temperature drop may be detected by measuringthe impedance of the tip and then determining the tip temperature byEquation (3) below. The impedance may be measured by turning off thepower to the cartridge/tip and measuring the voltage of the coil (in thecartridge) that is in thermal contact with the tip. The impedance of thetip would then be the voltage of the coil times an impedance weightfactor (K in Equation (3)), which would depend on the tip type and isstored in a memory, for example, in the cartridge itself. In someembodiments, a temperature sensor may be placed in the cartridge todirectly read the temperature drop of the tip and communicate it to themicroprocessor.R _(imd) =R _(min) +R _(max)/(1+[k*e^(−T)])  (3).

Where, R_(imd) is the impedance value, R_(min) is a minimum value of theimpedance, R_(max) is a maximum value of the impedance, K is a weightfactor and T is delta temperature, that is the temperature differencebetween the tip and the load. The tip temperature drop is typically dueto heat transfer from tip to load at the beginning and could vary from6° to 48° depends on tip geometry, heater, and type of the tip. Rmin isthe minimum impedance value for the solder tip, before power is on atstartup. Rmax is the maximum impedance value for the solder tip, afterpower is on at startup for a predetermined amount of time, for example,after 2 seconds. These values are specific to the specific solder tipthat is being used and are stored in a memory accessible by theprocessor.

FIG. 3B depicts a graph for a change in impedance of a soldering tipover time, for three given power levels that are delivered by the powersupply unit to the soldering tip and three given temperatures of thesoldering tip. As explained above, this data may also be stored in thememory of the cartridge. Graph 318 is for a small power, graph 312 isfor a large power and graph 314 shows a medium power. Moreover, graph310 is for a small, graph 316 is for medium temperature and graph 320 isfor a large temperature.

In some embodiments, the temperature drop may be detected by defining athermal efficiency factor for each given tip geometry and heatermaterial (stored in a memory, in the cartridge or outside of thecartridge), as shown in Equation (4) below. If power draws higher thanTE_factor, the system determines an abort in the process by, forexample, turning on a red LED, activating a haptic device, or activatinga sound-emitting device.TE_factor=TipMass*TipStyle*HTR_factor*Const  (4),

where, TipMass is the copper weight (mg), which is 0.65 for a LongReachtip, 1 for a Regular tip, and 1.72 for a Power tip. TipStyle refers tothe distance from the tip of tip to the heater in the cartridge. Forexample, according to data for some soldering tips currently availablein the market, TipStyle is 20 mm for a “LongReach” tip, 10 mm for a“Regular” tip, and 5 mm for a “Power” tip. HTR_factor is the heatertemperature times a factor (e.g., 0.01), which is given (predetermined),based on the type of the heater. Const=4.651*10⁻³ for all types ofheaters. For instance, the HTR_factor may be 800 F*0.01=8; 700 F*0.01=7;600 F*0.01=6; or 500 F*0.01=5 for various heater types. These parametervalues may be stored in a memory (e.g., NVM) of the soldering iron,soldering station, or within the cartridge itself.

Referring back to FIG. 2, in block 210, a thermal efficiency check isperformed to ensure that the tip geometry/temperature and the load arematched, based upon tip temperature drop within a predetermined timeperiod, for example, the first 2-3 seconds of the soldering event (e.g.,according to Equations (3) or (4), or a temperature sensor). Forinstance, there is a match when the max power after 2 seconds from thestart of the soldering is less than or equal the thermal efficiencyfactor of the solder tip being used. The parameters may be retrievedfrom the NVM.

In some embodiments, the thermal efficiency check process monitors theheat transfer and power recovery of the soldering station with respectto the tip and the load. Each tip type has its own thermalcharacteristic, which is a function of the tip temperature, mass, andconfiguration/style. For various tip types, their thermal characteristicand efficiency factors (TEs) are stored in a memory in the cartridge oroutside of the cartridge.

During the first period of time (e.g., 2-3 seconds), the power to thetip is measured (e.g., from the power supply) and compared with the TEof the tip. If the measured power is greater than a threshold value, forexample, 95%+/−10% of TE_factor, it means that the tip is too small orthe load is too large, because they require a lot of power. In thiscase, the thermal efficiency check fails (210 a), the process is abortedin block 226 and optionally one or more indicators, for example, a redLED, a haptic device and/or a sound-emitting device, are turned on. Ifthe thermal efficiency check passed (210 b), the process proceeds to theoptional block 212 where a passing indicator, such as a green LED and/ora beep, is turned on to let the operator or the robot program know thatthe thermal efficiency check process has passed.

In block 214, the liquidus temperature is detected based on thefollowing heat transfer equation.ΔT=P*TR  (5),

where, ΔT is the tip temperature minus the load temperature, P is the(electrical) power level to the tip, and TR is the thermal resistancebetween the tip and the load that may be retrieved from the NVM.

Since load temperature continues to increase until it reachesequilibrium, ΔT decreases throughout the soldering action. Also, powerto the tip increases when the soldering event first starts. Therefore,TR will be decreasing, as shown below. Once liquidus occurs, TR isstabilized and thus the power to the tip P now starts decreasing, asshown below. Accordingly, to detected liquidus temperature, the changestate in the power delivered to the soldering tip is observed.ΔT↓=P↑*TR↓ΔT↓=P↑*TR˜

In block 216, it is checked to see if the power is at a peak anddeclining. If not, the process is timed out (216 a) and aborted in block226. If the power to the tip, measured from the power supply, is at apeak and declining, the process proceed to block 218 to turn on anindicator, for example, an LED and/or a beep sound. When the power is ata peak and declining, it means that the solder event is at liquidusstate.

In Block 220, the Thickness of the IMC is Determined by the FollowingEquation.IMC=1+(k*ln(t+1))  (6),

where k is a weight factor for the type of solder being used (providedby the manufacturer of the solder and stored in the memory) and t is thesample/sensing interval time, for example 100 ms to determine the IMCthickness at a given time after liquidus. For example, K is constantwith a value of 0.2173, t is 0.1 second, that is, IMC is calculated at0.1 s intervals to avoid over shooting for small loads. That is, the tipcools as it heats the solder joint and as the heater tries to reheat thetip, the temperature may be overshooting from its set (desired) value.Typically, the thickness of the IMC may vary between 1-4 um.

Generally, the thickness of the IMC of the solder joint would be afunction of time and temperature. When the temperature is at meltingpoint of the solder load (e.g., at 220-240° C.), it does not have asubstantial impact on the thickness of the IMC of the solder joint.Accordingly, Equation (6) is based on only time and a fixed temperature.

FIG. 4A illustrates a graph for the thickness of the IMC of the solderjoint versus time, for the weighing factor k=0.2173, which is obtain byexperimentation, using many solder joint and IMC thickness measurements.As depicted in FIG. 4A, the IMC thickness increases over time, based onexperimental data.

Referring back to FIG. 2, block 222 checks to see whether within apredetermine amount of time (cooling period), the determined thicknessof the IMC is within a predetermined range, for example, 1 um to 4 um.If it is, the processes proceeds to block 224, where the operator isinformed. If the result of the test in block 222 is false, the processis timed out (222 b) and aborted in block 226.

In some embodiments, the invention provides the operator with anindication of successful or potential non-successful joint formation,along with the ability to collect the intermetallic joint information,and the operational parameters for that particular joint for postprocessing. Indication can be accomplished via visual means, audiblemeans, and/or vibration of the handpiece.

A debug mode (block 228) is used, for example, by a process engineer tokeep track of the steps involved during a solder event. To enter thedebug mode, a user needs to turn the debug mode on.

FIG. 4B illustrates a graph for the thickness for the IMC versussoldering time. As depicted, graph 402 is for a temperature of 300° C.with Y=0.176X+1.242, graph 404 is for a temperature of 275° C. withY=0.044X+1.019, and graph 404 is for a temperature of 220° C. withY=0.049X+0.297, where X is the time and Y is the IMC thickness. Theconstant numbers are derived from multiple experimentations. As shown, abreak out of the IMC thickness happens at three different temperatureranges. Since the thickness of the IMC is a function of time andtemperature, as temperature rises, the IMC grows larger, as a linearfunction. Depending on the application, any of these curves may be usedto determine the weighing factor, K, in Equation (6). For example, for asoldering application with SAC305 tip (the specification of which may bestored in the NVM of the cartridge), graph 404 is used.

FIG. 4C shows an IMC layer with a scale of 10 um. The vertical arrowsare where the IMC thickness measurement may be performed. As describedabove, the present invention detects liquidus temperature, determinesthe thickness of the IMC and ensures that a desired thickness isachieved.

This way, the embodiments of the present invention ensure a good bondingand electrical connection between two metals by calculating theintermetallic thickness and therefore prevent a bad joint in earlystages. Moreover, the invention provides instant feedback (by theindicators) to operators on joint quality and process issues and thusthe operators have the ability to track information on joint quality forpost analysis. The operators can change or select from a menu differentparameters to meet certain application requirements.

In some embodiments, when a self-regulated temperature feedbacktechnology is utilized, there is no requirement for calibration of thesystem at customer site. The invention also provides the capability tohelp the operators to identify whether they are using an impropertip/cartridge combination for a soldering event. For example, theinvention is capable of informing the operator (e.g. Via LED,sound-emitting device, haptic device, etc.), when the solder tip is notcapable to deliver sufficient energy required to bring the load to amelting point after a predetermined time (e.g., 2 seconds) from thestartup based on the thermal efficiency threshold stored in NVM.

In some embodiments, the invention uses at least two high resolutioncameras to capture two or more 2D images, obtain a 3D image from those2D images (utilizing various known techniques), use the 2D and 3D imagesto detect liquidus stage and then calculate the amount of solder filledthrough the via hole (barrel) for through hole components, or the amountsolder spread out around the components for surface mount components.

FIG. 5 is an exemplary process flow for liquidus detection andconnection verification using images from a plurality of cameras,according to some embodiments of the present invention. In someembodiments, at least two high resolution cameras are placed close tothe solder joint at two different locations to capture 2D images of thesolder joint from two views (angles), before and after the solderingevent. The liquidus is detected from comparison of the 2D images. Then,in the case of through hole components, the volume of the through holebarrel (barrel) is determined from 3D images generated from the 2Dimages. In the case of surface mounted (SMT) components, the surface ofthe barrel on the PCB is determined from the 2D images. As shown inblock 502, two images of the soldering area (joint) are captured by thetwo cameras, before the soldering event to generate two referenceimages, as depicted in FIG. 6A. In block 504, a 3D reference image ofthe soldering area is generated from the two reference images, beforethe soldering event, by well know methods.

In block 506, the volume of the barrel V_(b) for through hole and/or thesurface area of the barrel S_(b) for SMT component are determined fromthe 3D reference image to determine how much solder is need to fill thebarrel or the surface area of the barrel. The surface of the barrel mayalso be determined from the 2D images, depending on the cameraspositions. For example, knowing the distance and the angle of eachcamera to the solder joint, the distance of any point (e.g., points onthe perimeter of the barrel surface) may be determined, using simpleknown trigonometry. Also, having a second (stereo) camera, provides atlea four points to be used for volume determination. There are alsoknown software tools (e.g., computer vision software) that are capableof measuring the volume (and surface areas) from 3D images. For example,Image-Pro Premier 3D™ and Image-Pro Plus™ from MediaCybernetics™ iscapable of measuring the properties of multiple materials within avolume and easily discover percent composition, material mass,orientation, diameter, radii, and surface areas. The tool is capable ofmeasuring object volume, box volume, depth, diameter, radii, and surfacearea. Several other tools with similar functionalities are alsoavailable and know to one skilled in the art.

Accordingly, the amount of solder needed to fill in the barrel or thesurface of the barrel is determined, depending on the type of thecomponent. Immediately after the soldering event is started, two currentimages of the soldering area is captured, in block 508. In block 510,the color value of each pixel in the 2D reference images is compared tocolor value of each corresponding pixel in the 2D current images, as thesoldering event progresses, to detect any color changes of the pixels inthe current images due to spread of the solder. Since the pixel value ofthe solder color is known, this the process can determine whether apixel is a solder pixel, i.e., contains solder, as shown in FIG. 6B.

In block 512, the processes in blocks 508 (FIG. 6C) and 510 are repeateduntil all the pixels in the current images are determined to be pixelsof the dispensed solder, that is, the liquidus is now detected, asdepicted in FIG. 6D. The process in block 512 is timed out after apredetermined amount of time (e.g., 8 seconds), if not all the pixels inthe current images are determined to be pixels of solder. When all thepixels in the last two current images are determined to be pixels of thedispensed solder (within a tolerance range), the liquidus is detected,in block 514.

After the detection of the liquidus, the last current image from eachcamera are processed to generate a 3D current image, in block 516. Then,the volume of the dispensed solder V_(s) is determined from the 3Dcurrent image, by one or more of Equations (7) to (9), in block 518. Inblock 520, the calculated volume of the dispensed solder V_(s) iscompared to the determined amount of solder needed to fill in the barrel(i.e., V_(b)) or the surface area of the barrel (i.e., S_(b)) todetermine how much of the dispensed solder is dissipated into the barrelor on the surface area of the barrel. This process (block 520) isrepeated in block 522, until the dispensed solder has filled the barrelor the surface area of the barrel. That is, the volume of the visibledispensed solder has reached (V_(s) Vb) or (V_(s) S_(b)), within apredetermined tolerance range. The process in block 522 is timed outafter a predetermined amount of time (e.g., 8 seconds). An indicator(e.g., a LED and/or beep) is then turn on to notify the operator thatthe connection is now formed by filling all of the barrel or the surfaceof the barrel with the dispensed solder.

In other words, in the case of a through hole component, when thecalculated volume reduces to a predetermined amount that is needed tofill the barrel and within a pre-defined tolerance for through holecomponent, a good solder joint is formed, as shown in FIG. 7A. In someembodiments, the calculation of the height and volume of the solderjoint is performed based on the following equations.V _(lead) =πr _(lead) ² h  (7)V _(barrel) =πr _(barrel) ² h  (8)V _(required) =πh(r _(barrel) ² −r _(lead) ²)  (9)

Where, V_(lead) is the volume of component lead; V_(barrel) is thevolume of through hole barrel; V_(required) is the volume of solderrequired to fill the barrel, r_(lead) is the (though hole) componentlead radius; r_(band) is through hole barrel radius; and h is the boardthickness, as shown in FIG. 7A.

FIG. 7A shows some exemplary solder joints, the image of which iscaptured by the two cameras, for through hole components, according tosome embodiments of the present invention. FIG. 7B shows some exemplarysolder joints, the image of which is captured by the two cameras, forsurface mount components, according to some embodiments of the presentinvention. In this case, the invention compares the height of the entireload to a predetermined reference height (a desired height) to form aparabolic or linear shape. Once the identified shape area is equivalentto a predefined percentage of the load (barrel) surface area within apredefined tolerance, a good solder is formed for the surface mountcomponent. As shown in FIG. 7B, for a larger surface mount component,the solder joint is formed on the side of the component as a parabolicshape. However, for a smaller surface mount component, the solder jointis formed on the side of the component as a linear shape since thecamera can only capture a linearly filled area due to the small size ofthe component.

It will be recognized by those skilled in the art that variousmodifications may be made to the illustrated and other embodiments ofthe invention described above, without departing from the broadinventive step thereof. It will be understood therefore that theinvention is not limited to the particular embodiments or arrangementsdisclosed, but is rather intended to cover any changes, adaptations ormodifications which are within the scope and spirit of the invention asdefined by the appended claims.

What is claimed is:
 1. An intelligent soldering cartridge comprising: ahousing; a solder tip; a heater for heating the solder tip; a processorfor determining a thickness of an intermetallic compound (IMC) of asolder joint being formed by the solder tip, and generating anindication signal indicating that a reliable solder joint connection isformed when the thickness of the IMC is within a predetermined range;and an interface for transmitting the indication signal.
 2. Theintelligent soldering cartridge of claim 1, further comprising a storagedevice for storing information about characteristics of the cartridge,wherein the processor determines the thickness of the IMC using some ofthe retrieved information and an amount of power delivered to the soldertip.
 3. The intelligent soldering cartridge of claim 2, wherein thestorage device comprises one or more of non-volatile memory (NVM) and aradio frequency identification device (RFID).
 4. The intelligentsoldering cartridge of claim 2, wherein information aboutcharacteristics of the intelligent soldering cartridge includes one ormore of a part number, a serial number, an indication of time of usageof the intelligent soldering cartridge, a mass of the solder tip, asolder tip configuration, an authentication code, and thermalcharacteristics of the solder tip.
 5. The intelligent solderingcartridge of claim 4, wherein information about characteristics of theintelligent soldering cartridge further includes one or more ofinformation about a change in the temperature of the solder tip overtime for various load sizes, contact surface of the solder tip withsolder, distance of the solder tip from the heater, number of solderingevents that have already been performed by the solder tip, total usagetime of the solder tip, and date of manufacturing of the intelligentsoldering cartridge.
 6. The intelligent soldering cartridge of claim 1,further comprising a temperature sensor for measuring a temperature ofthe solder tip.
 7. The intelligent soldering cartridge of claim 6,wherein the temperature sensor periodically measures the temperature ofthe solder tip and feeds the information to the processor, and whereinthe processor adjusts the temperature of the solder tip when saidtemperature changes from a predetermined value.
 8. The intelligentsoldering cartridge of claim 1, further comprising a potentiometer formeasuring an impedance of the solder tip.
 9. The intelligent solderingcartridge of claim 1, wherein the interface is one or more of a wiredinterface and a wireless interface.
 10. A handheld soldering ironincluding the intelligent soldering cartridge of claim 1 for solderingwork pieces.
 11. An automatic soldering station including theintelligent soldering cartridge of claim 1 for soldering work pieces.12. An intelligent soldering cartridge comprising: a housing; a soldertip; a heater for heating the solder tip; a processor for receiving a 3Dimage of a solder joint being soldered by the intelligent solderingcartridge, determining a volume of a dispensed solder from the 3Dcurrent image, comparing the volume of the dispensed solder to an amountof solder needed to fill in a barrel of a hole for a through holecomponent, or to fill in a surface area of a pin footprint for a surfacemount component to determine how much of the dispensed solder isdissipated onto the barrel or on the surface area of the pin footprint,and generating an indication signal indicating that a reliable solderjoint connection is formed when the dispensed solder has filled thebarrel or the surface area of the pin footprint within a predeterminedtolerance; and an interface for transmitting the indication signal. 13.The intelligent soldering cartridge of claim 12, wherein the storagedevice is one or more of non-volatile memory (NVM) and a radio frequencyidentification device (RFID).
 14. The intelligent soldering cartridge ofclaim 12, wherein information about characteristics of the cartridgeincludes one or more of part number, serial number, total usage of thecartridge, solder tip mass, solder tip configuration, authenticationcode of the cartridge, and thermal characteristics of the solder tip.15. The intelligent soldering cartridge of claim 14, wherein informationabout characteristics of the cartridge further includes one or more ofinformation about a change in the temperature of the solder tip overtime for various load sizes, contact surface of the solder tip withsolder, distance of the solder tip from the heater, number of solderingevents that have already been performed by the solder tip, total usagetime of the solder tip, and date of manufacturing of the cartridge. 16.The intelligent soldering cartridge of claim 12, wherein the interfaceis one or more of a wired interface and a wireless interface.
 17. Theintelligent soldering cartridge of claim 12, further comprising atemperature sensor for measuring a temperature of the solder tip. 18.The intelligent soldering cartridge of claim 17, wherein the temperaturesensor periodically measures the temperature of the solder tip and feedsthe information to the processor, and wherein the processor adjusts thetemperature of the solder tip when said temperature changes from apredetermined value.
 19. A handheld soldering iron including theintelligent soldering cartridge of claim 12 for soldering work pieces.20. An automatic soldering station including the intelligent solderingcartridge of claim 12 for soldering work pieces.